Experiment 2: Concentration Gradients and Membrane Permeability
In this experiment, you will dialyze a solution of glucose and starch to observe:
An indicator is a substance that changes color when in the presence of a specific substance. In this experiment, IKI will be used as an indicator to test for the presence of starch.
(5) 100 mL Beakers
*15.0 cm Dialysis Tubing
*You Must Provide
1. Measure and pour 50 mL of water into a 100 mL beaker using the 100 mL graduated cylinder. Cut a piece of dialysis tubing 15.0 cm long. Submerge the dialysis tubing in the water for at least ten minutes.
3. Make the glucose/sucrose mixture. Use a graduated pipette to add 5 mL of glucose solution to a third 100 mL beaker and label it “dialysis bag solution.” Use a different graduated pipette to add 5 mL of starch solution to the same beaker. Mix by pipetting the solution up and down six times.
4. Using the same pipette that you used to mix the dialysis bag solution, remove 2 mL of the dialysis bag solution and place it in a clean beaker. This sample will serve as your positive control for glucose and starch.
a. Dip one of the glucose test strips into the 2 mL of glucose/starch solution in the third beaker. After one minute has passed, record the final color of the glucose test strip in Table 3. This is your positive control for glucose.
b. Use a pipette to transfer approximately 0.5 mL of IKI into the 2 mL of glucose/starch solution into the third beaker. After one minute has passed, record the final color of the glucose/starch solution in the beaker in Table 3. This is your positive control for starch.
5. Using a clean pipette, remove 2 mL of water from the 82 mL of water you placed in a beaker in Step 2, and place it in a clean beaker. This sample will serve as your negative controls for glucose and starch.
a. Dip one of the glucose test strips into the 2 mL of water in the beaker. After one minute has passed, record the final color of the glucose test strip in Table 3. This is your negative control of glucose.
b. Use a pipette to transfer approximately 0.5 mL of IKI into the 2 mL in the beaker. After one minute has passed, record the final color of the water in the beaker in Table 3. This is your negative control for starch.
Note: The color results of these controls determine the indicator reagent key. You must use these results to interpret the rest of your results.
6. After at least ten minutes have passed, remove the dialysis tube and close one end by folding over 3.0 cm of one end (bottom). Fold it again and secure it with a rubber band (use two rubber bands if necessary).
7. Test to make sure the closed end of the dialysis tube will not allow the solution to leak out. Dry off the outside of the dialysis tube bag with a cloth or paper towel. Then, add a small amount of water to the bag and examine the rubber band seal for the leakage. Be sure to remove the water from the inside of the bag before continuing.
|Figure 4:Step 9 reference.|
9. Place the filled dialysis bag in the 100 mL beaker filled with 80 mL of water, leaving the open end draped over the edge of the beaker as shown in Figure 4.
10. Allow the solution to sit for 60 minutes. Clean and dry all materials except the beaker holding the dialysis bag.
11.After the solution has diffused for 60 minutes, remove the dialysis bag from the beaker and empty the contents of the bag into a clean, dry beaker. Label the beaker “final dialysis bag solution.”
12. Test the final dialysis bag solution for the presence of glucose by dipping one glucose test strip into the dialysis bag. Wait one minute before reading the results of the test strip. Record your results for the presence of glucose in Table 4.
13.Test for the presence of starch by adding 2 mL IKI. After one minute has passed, record the final color in Table 4.
14. Use a pipette to transfer 8 mL of the water in the beaker to a clean beaker. Test the beaker water for the presence of glucose by dipping one glucose test strip into the beaker. Wait one minute before reading the results of the test strip, and record the results in Table 4.
15.Test for the presence of starch by adding 2 mL of IKI to the beaker water. Record the final color of the beaker solution in Table 4. Get PHYSICS homework help today
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